Plant Pathology Science

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Arbuscularfungi are root symbiontsof 80% of plants, such as most field crops and fruit trees. They establish in root tissue, arbuscule in endodermis cells, and an extramatrical fine hyphal net. These fungi byincreasing absorption of water and nutrient elements for plants, making changes in chemical constituents of plant tissues, competition with pathogens for nutrients and establishment site, structural changes in roots, alleviation of environmental stresses, and increasing population of useful bacteria in soil, help management of diseases caused by fungi, fungal like organisms, nematodes, bacteria, phytoplasmas and physiological disorders. Collection, identification, purification, propagation, and inoculation of these useful fungi to plants, can decrease usage of chemical fertilizers and pesticides that are harmful to consumers of agricultural products as well as to the environment

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In 2005, Circular to elliptical brown necrotic leaf spots, were observed on young leaves of Banana(Musa acuminata L.) plantion under plastic cover in Mazandaran&Gorgan provinces. The rhizomes and pseudostems were not affected. A gram-negativebacterium with yellow mucoid colonies was isolated from the leaves on sucrose and glucose nutrient agar. All isolates were negative in oxidas, and positive in catalase reaction. Non of isolates did not produce green or blue pigment on KB medium. On the basia of phenotypic charachteristics pathogenicity test was confirmed with inocoulation of bacterial suspension to Banana plants. The causal agent of bacterial necrotic and leaf spot of banana was recognized asXanthomonascampestris. This is the first report ofbacterial necrotic and leaf spot of banana in Iran.

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In last decades, development of Biology science, importance of protection of environmentand high demand to the nutrients is caused that usage of the biological materials, in order to increase crop yield, have been viewed by researchers. Some of the Bacilli, Rhizobia and Trichoderma species are distinguished as Plant Growth Promoting. These micro-organisms with colonization and abundant sporulation in soil especially in rhizosphere of most of the cultivated and non-cultivated plants not only decrease the pathogenic agents, but also increase growth of the plants by bio-chemical mechanisms. With attention to isolate and study of many Trichoderma species in Iran, importance of performance researches about plant growth promoting effects of theTrichoderma species is necessary. In this paper, review of the plant growth promoting effects of Trichoderma is presented.

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The importance of plant protection in modern agriculture increases as crop yields and concerns about production quality rise. Plant protection should be sufficiently effective, affordable and considerate of the environment. The integration of biological and chemical control has a potential for success because of a possible synergistic effects. It is necessary to look for organisms suitable for use in biological control, and in order to study the mechanisms of their action and the optimal conditions for incorporating such agents in plant protection and integrated management systems. One of such microorganisms is PythiumoligandrumDrechslerthatbelongs to the phylumOomycetes. This soil-resident saprophytic microorganism can be parasitic and hyperparasitic on many fungi within the same or other classes. The antagonistic activity of P. oligandrumis a multifaceted process which depends on the target species involved. P. oligandrumis nonpathogenic on 12 species of crops that belong to six families. It occurs on the root surface together with plant pathogenic fungi, predominantly in the regions of hypocotyl – taproot without penetrating the plant tissues. The plant growth is reportedly stimulated by this species. P. oligandrum can be utilized for biological control on a wide spectrum of crop plants. Different methods of application have been developed. The most effective activity of this microorganism is the mycelial growth inhibition of the plant pathogenic fungi.

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Vegetables are attacked by different pests and diseases during their growth. Some fruits such as cucumber have sprayed regularly against diseases like Pseudoperonosporacubensisspecially in humid areas, and after a short time the cucumber are picked up and the amount of pesticide residue are measured and comparing with Maximum Residue Level (MRL). In this research the amount of Mancozeb fungicide has quantified in cucumber samples in Sari district. So in this order 26 samples of cucumber are collected and were carried to the laboratory. Samples of fruits are weighted and washed by using of n- hexan in Suksoleh device. After concentrating the obtained solution put in spectrophotometer set for measuring the optical density with 280 nanometer wave lengths and the amount of uv absorbance of samples and standard solutions were checked. The obtained numbers was changed into all right amount of mancozeb by using Excel software and Cx= α. Cs / β. Vx equation. Results showed that the amount of remained mancozeb fungicide was less than maximum residue limit in 77 percent of samples and more than maximum residue limit in 23 percent of samples in these periods. Also it defined among the samples which have had residue higher than standard limit, just 2 samples have been increased more than 1 milligram per kilogram.

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The Pepper (Capsicum annuum) is one of the important field crops in the worlds, which its cultivation has been developed, because of its food value and consumptions. But, there are certain diseases, which limited the growth and productivity, out of which the fungal diseases are of high severity. Thus, for this very purpose, a survey was conducted in the pepper growing areas including field and glass houses for fungal diseases identification in Isfahan provinces. The infected pepper plants were collected in the plastic bages and transferred, into the lab. The macro and microscopic studies indicated that there are severed fungal diseases infecting the pepper plant on the areal parts, including Powdery mildews, Downy mildews, Sclerotinia stem rot, early blight and Botrytis molds. Except the Downy and Powdery mildews being obligate parasite, which cannot be cultured the rest were culture from the margin in the infected parts, where the disease were under development on PDA for purification and identifications through tip culture. The results revealed that, there are several fungal species involving including Peronosporatabacina for Downy mildew, Levielullatauricafor Powdery mildew, Early blight, Alternariaalteanataand A. solani, fruit rot, Botrytis cinerea and stem rot due to Sclerotiniasclerotiorum from areal parts.

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Early blight is an important worldwide disease of tomato that farmers must have frequent spray chemicals to control it. One way to reduce the use of pesticides, costs of production and the risk of environmental pollution, spraying based on forecasting of TOMCAST system, which is based on the time of wet leaves and temperature during tomato growing season in each region, predict disease severity , and determine suitable time of spraying. Application this system, in some countries considerably reduced pesticides usage on tomato. This system predict time of spraying when needed and has maximum effect. By using this forecasting method in Iran, can reduce pesticides usage on this freshly consume fruit, efficiency of using pesticides, and increase yield. 

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Genetic engineering has begun about 160 years ago with discover inheritance laws of biological traits, isolation and purification of DNA from inner cell, replication and propagation of its pieces with polymerase chain reaction in vitro, identification and purification favorable genes and transfer them with Agrobacterium  tumefaciens bacterium, or directly to plants cell, by gene gun, and produce whole transgenic  plant, from gene modified cell with tissue culture methods innovation and fully developed in recent 4 decades. With this technology transfering  favorable genes, without accompaniment with  unwanted genes, into plants is possible, and resistance transgenic plants to fungal, bacterial, viral and nematodes, and tolerant to environmental stress produced. Genetic engineering has created hope for better plants diseases management and increase agricultural production to meet food needs of a growing human population.

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Citrus gummosis disease cause canker accompanied by gum exudates, crown and root rot, twig dieback, and decline of citrus trees. This disease has been reported from Khuzestan and Fars provinces, now infected by in parts of Kohgiluyeh and Boyerahmad province (southwest Iran), namely: Molabarfi, Bidestan, Posht-e-koh, Tol-e-mavizi, Bidzard, Chaharbish-e-olia and Chaharbish-e-sofla from Gachsaran town and Cheshm-e-belghis, Dehborji, Spar and Marin from Kohgiluyeh town. Sour lemon, sweet lemon, big sour lemon and orange were more infected respectively. Pathogen identified as Phytophthora nicotianae. As it is epidemic in this province for planting diseased seedlings, incorrect planting method, stalk sensitivity, incorrect irrigation method, can manage by planting healthy certified seedlings on sour orange stalk, correction planting and irrigation methods, chemical control, and biological control with antagonistic fungi or bacteria.

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Trichoderma form-species are among of the important antagonists of plant pathogenic fungi and also induce resistance in field crops. Therefore their isolation and identification could be helpful for applying them in biological control. They isolate by pour soil diluted suspension on Dawet, Peptone – Rose Bengal, or modified Potato- Dextrose-Agar mediums. Species can identify based on colony characteristics, growth characteristics and morphological characteristics of conidiophores, phialids, and conidia. Eighty-five isolates of Trichoderma from 25 soil samples, from 8 regions of the Fars province sugar beet fields, isolated and purified with this method. With studied their characteristics eight form-species of Trichoderma identified with names: T. asperellum, T. atroviride, T. brevicompactum, T. harzianum, T. longibrachiatum, T. spirale, T. tomentosum and T. virens . Methods of isolation, identification and morphological characteristics of these fungi described.

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Fusarium ear rot is one of the most important diseases of corn in Iran. This disease cause by Fusarium moniliforme fungus. Its symptoms are pink to red spots on ear, cause it completely rot and eventually loss of yield quantity and quality. Identification and cultivation resistant or semi-resistant corn hybrids is the best management method of this disease. Artificial infection of maize hybrids with fungal suspension of causal agent is an affective method to study their reactions, determine base on disease severity index (%DS). According to research conducted in Iran, between 12 planting hybrids, 2 hybrids K3493 / 1 × K18 and KLM 77029/8-1-2-3-2-3 × MO17 are resistant, and 9 are semi- resistant . With extension, cultivation of these hybrids, can manage the disease and increase the quality and quantity of maize hoped.

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Root and crown rot is an important disease in Kohgiluyeh and Boyerahmad province peach orchards. Its signs are wilting, general weakness, loss of foliage and sometimes sudden wilt and death of the tree. To isolate the pathogen, used corn meal-agar with antibiotics, Delvasid, Ampicillin and rifampicin medium. Pathogen is Phytophthora cactorum. For pathogenesis test, 2 inoculation methods, to a tree branch or contaminated soil around the roots and crown of seedling is used. Inoculation roots and crowns of seedlings and saplings of six varieties of peaches with this pathogen, showed that Takheh is resistant, Alberta, Redhoon and Mashhad red peach are semi-resistant, Angiri and J.H.Hill are sensitive to the disease

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The soft rot causal bacteria, species of Pectobacterium and Dickeya, are important pathogens of plants, which have worldwide distribution. These bacteria are very broad host range and cause plant tissues rot . Diseases caused by these bacteria in the form of soft rot, black stem, bulb rot and leaf spot of corn, rice, canola, sugar beet, potatoes, banana, dates, carrots, cabbage, onions, turnips, peppers, philodendron, pandanus, dieffenbachia, Cyclamen, Iris, Aglaonema, Dracaena, Gladiolus, Ficus, ornamental cactus, and Orobanche have been reported from Iran. Some varieties of field crops such as corn, tomatoes, potatoes and sugar beet, as tolerant to these bacteria in Iran.

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Powdery mildew fungi are important obligate parasites of plants. They produce white cover on aerial parts of host plants, which then turn to yellow. The diseased plant becomes yellow and then wilted result in reducing quality as well as quantity of products in field and vegetable crops and also fruit trees. Among all of the control measures against powdery mildew, the most common method is application of the chemical fungicides, after disease incidence. Regarding to the hazards of agrochemicals and also considering the probability of incidence of resistant races of the pathogen, the biological control is considered as a safe and useful method for controlling the disease. The fungi Ampelomyces quisqualis, Pseudozyma flocculosa and Lecanicillium longisporum the bacterium Bacillus subtilis the mite Tydeus lambi and twenty-spotted lady beetle Psyllobora vigintimaculata , have been used effectively against the powdery mildew of cucumber, squash, tomato, pepper, grape and rose. Some of these biological agents have been introduced to the market, commercially.

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There are some strategies for adaptation to environmental changes in plants, including a range of molecular-biochemical and also intent or induced mechanisms. The proper response of plant is occurred when it receives extracellular signals and transfers those inside the cell. Ethylene, identified as a plant hormone which regulates the plant reactions under some circumstances. Ethylene production has been enhanced in response to biological stresses like plant infection by pathogens or herbivores attack. Most of induced defense genes are regulated by transduction pathways signal. The biosynthesis pathway of ethylene from the amino acid methionine has been studied well. In this pathway, the produced ethylene activates the resistant genes resulting to incidence of plant resistance. The responsible genes in rice and also the ethylene-expressed resistance genes have been discussed in this review.

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Regarding to the need of improving the quality and quantity of agricultural products, the science of plant protection has been taken under consideration. Accurate identification and detection of plant pathogens is one of the best ways for successful plant disease management. One of the useful methods is analysis of the volatile organic compounds, which spread from diseased plants. In this method, specificity of the volatile organic compounds and also the factors that affect the identifying of plant diseases and effective methods on these compounds are important. First, these compounds should be collected and then be analyzed. The best method for analysis of these compounds is dynamic sampling followed by gas chromatography and using the proper probes. Although the high costs of the tools make it difficult to apply this method for agricultural purposes, but by using the statistical methods and estimations the costs can be decrease.

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DNA microarrays technology is a method for studying the gene expression in large scale, based on investigations of probes and targets hybridization. This technology can also be used for identification of different organisms. DNA microarrays are a set of probes linked to a solid phase as microscopic spots. After hybridization of targets to probes, hybridization level is calculated by means of different methods such as measuring refulgence of fluorescent dyes to determine gene expression level. A microarray examination has different steps: making DNA chips, preparing targets, performing hybridization, and gathering and analyzing data. DNA microarrays technology can be used in different fields of plant pathology such as identification of different species of fungi, bacteria, nematodes and viruses, and to study plant-pathogen interaction.

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Most nematodes are free-living. They live in oceans, fresh waters and soil and feed on bacteria, fungi and other nematodes. Some are predators and some are parasites of plants and animals. Some of the latter group are insect-associated. There are different types of relations between insects and nematodes. Beneficial nematodes that cause disease in insects are referred to as “entomopathogenic” and have the ability to kill the insects. Entomopathogenic nematodes from the genera Stein‌ernema and Heterorhabditis have proven to be the most effective as biological control organisms. Only the infective juvenile stage of entomopathogenic nematodes will survive in the soil, find and penetrate insect pests. In this paper, different types of association between nematode and insect with emphazing on entomopathogenic nematode species have been reviewed.

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Sexual reproduction of fungi is governed by the mating type (MAT) locus. Because two alternate forms (alleles) are completely dissimilar sequences and encoding different transcription factors, this locus is structurally unusual, yet they occupy the same chromosomal position. Genomic analyses facilitate the definition of MAT locus sequences in many species, so the knowledge of MAT locus structure and evolution has been significantly advanced in recent years. This important genomic feature has been studied most extensively in the largest phylum of the fungi, Ascomycota, which is the largest group of the plant pathogenic fungi. In this article we discuss the different aspects of mating type genes and their structure and organization in Ascomycota. Knowledge on the mating type genes may provide a great assistance to understanding the potential of phytopathogenic fungi for sexual cycle and consequently on genetic diversity in fungal populations. The proper data on sexual reproduction and genetic diversity of phytopathogenic fungi might be useful in different aspects of plant disease management.